Ford Expedition Check Engine Light On – Faulty Oxygen Sensors?

Reader Question I have a 1997 Ford Expedition and we replaced all 4 of the O2 sensors this spring (one at a time) and now they are all bad again. What can cause them to go bad? My engine is “boggy” when in the idle position, especially when air conditioner is on. Should I address this immediately?

Thanks!

Natalie J

Hey Natalie,

What do you mean by “boggy” that’s a new one on me. If the idle is rough (not nice and smooth) or the idle speed surges or fluctuates I would suspect you have a dirty throttle body and or dirty idle speed control motor, or a faulty idle speed control motor.

Changing all the o2 sensors is uncommon, doing it twice….either you have a misdiagnosis or something weird is up. The only thing I can really think of that would cause damage to the o2 sensors would be using some kind of fuel additives or a restriction in the exhaust system like a stopped up catalytic converter.

I am assuming the check engine light is coming on…which it should if you have bad o2 sensors, but the light might not come on if you have a dirty idle motor or throttle body.

How well do you trust your mechanic and his expensive diagnosis? Should you get a second opinion….I probably would.

Faulty o2 sensors can cause the check engine light to come on, poor fuel mileage and poor engine performance – lack of power, and probably cause you to fail an emissions test.

Blessings,
Austin C. Davis

Reader Follow Up

Austin,

Yes, the check engine light is on and the engine is just as you described it during idle. Surge and fluctuate. I am a single person and worry about getting taken advantage of.. First person I talked to said it was probably catalytic convertercausing them to go bad like that. Hmmm… We’ll see.. how much can you save in fuel mileage? Is this something I should address right away? Thank You for your response.

Natalie

Hello again Natalie

I would get a second opinion first before we can really determine the seriousness of the situation. Find a quality repair shop in your area that is capable of reading the onboard computer codes and diagnosing the problem.

You are probably ok to continue to drive like this for awhile. The fuel mileage could be hampered by as much as 50% IF the o2 sensors where really bad.

Let me know what you find out.

Blessings,
Austin C. Davis

3 Comments on "Ford Expedition Check Engine Light On – Faulty Oxygen Sensors?"

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  1. derek jay says:

    Natalie, I am a mechanic and have been for 15 years now. I know what you mean by “BOGGY”. The fellow who didnt know probally need not give anyone advice. The 1997 Ford Expedition model is the best. The problem you are having is a small problem perhaps. It may be anything frrom faulty 02 sensor to the valve covered gasket. Yes the “Valve covered Gasket. I have that model expedition and I had the same check engine light on, but I got to the problem and solved it quickly. So please make certain that its not leaking. Good Luck!

  2. Marc says:

    Natalie, I think you might not have a problem with your catalytic converter i recently replaced mine which was a pain to replace because its so far into the dashboard and i also had a professional mechanic check to make sure i had done it right. i did. the check engine light came on about 1-2 months afterwards still no idea what it could be. so good luck and if you fix your problem let me know =).

    sincerely, Marc.

  3. Marc says:

    Natalie, i think you might not have a problem with your catalytic converter i recently replaced mine which was a pain to replace because its so far into the dashboard and i also had a professional mechanic check to make sure i had done it right. i did. the check engine light came on about 1-2 months afterwards still no idea what it could be. so good luck and if you fix your problem let me know =).

    sincerely Marc.

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